Invert emulsion fluids, i.e. emulsions in which the non-oleaginous fluid is the discontinuous phase and the oleaginous fluid is the continuous phase, are employed in drilling processes for the development of oil or gas sources, as well as, in geothermal drilling, water drilling, geoscientific drilling and mine drilling. Specifically, the invert emulsion fluids are conventionally utilized for such purposes as providing stability to the drilled hole, forming a thin filter cake, lubricating the drilling bore and the downhole area and assembly, and penetrating salt beds without sloughing or enlargement of the drilled hole.
Oil-based drilling fluids are generally used in the form of invert emulsion muds. An invert emulsion mud consists of three-phases: an oleaginous phase, a non-oleaginous phase and a finely divided particle phase. Also typically included are emulsifiers and emulsifier systems, weighting agents, fluid loss additives, viscosity regulators and the like, for stabilizing the system as a whole and for establishing the desired performance properties. Full particulars can be found, for example, in the Article by P. A. Boyd et al entitled “New Base Oil Used in Low-Toxicity Oil Muds” in the Journal of Petroleum Technology, 1985, 137 to 142 and in the Article by R. B. Bennet entitled “New Drilling Fluid Technology-Mineral Oil Mud” in Journal of Petroleum Technology, 1984, 975 to 981 and the literature cited therein.
During the drilling process, it is not uncommon for the drilling fluid to encounter a water bearing formation and thus the ratio of oleaginous fluid to non-oleaginous fluid is less than optimal. In some cases, the formation of a difficult to break emulsion occurs and this is often referred to as the “slop”. The oil to water ratio in the slop may be 25/75 or 30/70 or similar such numbers. Using conventional methods of emulsion breaking it is possible to recover say a 60/40 ratio of oil to water fluid. This is then diluted with additional make up oil to achieve the desired ratio typically 80/20. One of the primary difficulties with this system is the use of emulsion breakers and surface tension breakers that are not environmentally friendly. That is to say the emulsion breakers and surface tension breakers of the prior art are harmful to aquatic life and thus may not be directly discharged without further treatment or disposal.
Any rig drilling with oil based/synthetic oil based drilling mud is likely producing between 20 to 40 cubic meters per day of slop water, also referred to as waste mud or gray water. The slop water usually may not be directly discharged into the sea because of its hydrocarbon content, which is usually higher than regulatory limits. Therefore the slop water needs to be transported in boat tanks to shore for disposal according to the local regulations. A large portion of this slop water may be classified as special waste.
Thus there exists a continuing need for skid-mounted apparatuses and methods to effectively break emulsions on an offshore rig in an environmental friendly manner thereby reducing the need to transport the slop water onshore.